I want to compare output impedance of TL780-05 and LM7805, and also AC output impedance. Which parameter indicates these?

Both are fixed 5V regulators.

I can only see that one of them has 1% accuracy and the other 4%.

  • 1
    \$\begingroup\$ AC output impedance for DC regulators? \$\endgroup\$ – Leon Heller Sep 14 '18 at 12:06

Both devices specify parameters called: -

  • Load regulation (how much the output may change under load)
  • Output resistance at 1 kHz (related to the above)

Neither device specifies the AC output impedance because it will be always assumed that the parallel output load capacitance will dictate that i.e. 10 uF at (say) 100 kHz has an effective AC impedance of 0.16 ohms.

  • \$\begingroup\$ Thanks can you also add your answer how can we compare the load regulation? Also this was my previous question electronics.stackexchange.com/questions/396036/… to be used with this ratiometric chip sensing.honeywell.com/… Maybe you would have an input thanks. \$\endgroup\$ – HelpMee Sep 14 '18 at 12:13
  • \$\begingroup\$ Thats why I was asking about AC output impedance. \$\endgroup\$ – HelpMee Sep 14 '18 at 12:14
  • \$\begingroup\$ Load regulation is worse when the mV specified in the data sheet for a given load change is worse for one device compared to another. \$\endgroup\$ – Andy aka Sep 14 '18 at 12:16
  • 1
    \$\begingroup\$ The 0.16 ohm is the impedance of a 10 uF capacitor at 100,000 hertz. In other words the HF AC output impedance of a voltage regulator is determined from about 100 kHz (ball park figure) and upwards by the output capacitor and not the silicon. \$\endgroup\$ – Andy aka Sep 14 '18 at 12:18
  • 1
    \$\begingroup\$ @user1234 no it must be there but remember that the capacitors impedance is shunted the the output impedance of the regulator and, at low frequency, it is a sub ohm value. As frequency rises the regulator output impedance rises but the cap impedance falls and so the baton of low impedance is passed from regulator to capacitor. \$\endgroup\$ – Andy aka Sep 14 '18 at 13:05

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.